Allowing the client to delete revisions breaks the "audit trail" functionality. This is not allowed in WordPress and shouldn't be allowed through the API.
While not recommended, a plugin may opt-in to the previous behavior by setting a custom 'delete_post' capability for the revisions post type.
Props dlh, danielbachhuber, TimothyBlynJacobs, azaozz, kadamwhite.
Fixes #43709.
git-svn-id: https://develop.svn.wordpress.org/trunk@45812 602fd350-edb4-49c9-b593-d223f7449a82